Backlighting units are widely used in all kinds of electrical apparatus, such as display apparatus. A display apparatus generally includes a display panel and a backlighting module for providing a backlight to the display panel. The backlighting module includes a light source and a plurality of optical films, such as light guide plate, a film, a reflector, a diffuser, and a quantum dot enhancement film (QDEF). The QDEF converts a wavelength of light. An invalidation portion along a cutting path may be generated when cutting the QDEF to a desired size by laser. The quantum dots in the invalidation portion are damaged and lose the ability to convert wavelength of light. Thus, a light from the light source with an original wavelength may leak from the invalidation portion causing a light leakage of the display apparatus. A light leakage of the display apparatus would be prevented by an improved structure.